Proteins, nucleic acids, or other biological species that have been electrophoretically separated in a slab gel are often transferred to a blotting membrane formed of nitrocellulose, nylon, polyvinyl difluoride, or similar materials prior to identification and quantification. A common transfer technique is electroblotting, in which flat surfaces of the gel and membrane are placed in direct contact. An electric current is then passed through both the gel and the membrane in a transverse direction, thereby transferring the species in a manner similar to that by which the species were mobilized within the gel. When the species are DNA fragments, the transfer is termed a Southern blot after its originator, the British biologist Edwin M. Southern. By analogy, the transfer of RNA fragments is termed northern blotting, and the transfer of proteins or polypeptides is termed western blotting. Still further examples are “eastern” blots for post-translational modifications, and “far western” blots for protein interactions.
Electroblotting can be performed in either a wet, dry, or semi-dry format. In wet blotting, the gel and membrane are layered over each other in a stack which is immersed in a transfer buffer solution in a tank on whose walls are mounted wire or plate electrodes. The electrodes are then energized to cause the solutes to migrate from the gel to the membrane. In semi-dry blotting, filter papers wetted with the transfer buffer solution are placed on the top and bottom of the stack with the gel and the membrane in between to form a “blotting sandwich.” The electrodes are then placed in direct contact with the exposed surfaces of the wetted filter papers. In dry electroblotting, no liquid buffers are used other than those residing in the gels. Descriptions of wet, dry, and semi-dry electroblotting and the associated materials and equipment are found in Margalit et al. (Invitrogen) United States Patent Application Publications No. US 2006/0272946 A1 (Dec. 7, 2006), No. US 2006/0278531 A1 (Dec. 14, 2006), and No. US 2009/0026079 A1 (Jan. 29, 2009); Littlehales (American Bionetics) U.S. Pat. No. 4,840,714 (Jun. 20, 1989); Dyson et al. (Amersham International) U.S. Pat. No. 4,889,606 (Dec. 26, 1989); Schuette (Life Technologies, Inc.), U.S. Pat. No. 5,013,420 (May 7, 1991); Chan et al. (Abbott Laboratories), U.S. Pat. No. 5,356,772 (Oct. 18, 1994); Camacho (Hoefer Scientific Instruments), U.S. Pat. No. 5,445,723 (Aug. 29, 2005); Boquet (Bertin & Cie), U.S. Pat. No. 5,482,613 (Jan. 9, 1996); and Chen (Wealtec Enterprise Co., Ltd.) U.S. Pat. No. 6,592,734 (Jul. 15, 2003).
In all electroblotting formats, one or more aqueous solutions contact or are contained within the electrophoresis gel or blotting membrane. When metal (e.g., platinum, silver, lead, copper, or aluminum) electrodes are used for electroblotting, electrochemical reactions occur at the interface of each electrode with these solutions. The reactions can involve water electrolysis, producing O2 gas, hydrogen ions, and hydrogen peroxide at the anode, and H2 gas and hydroxide ions at the cathode. Electrochemical reactions can also ionize the electrodes, causing metal ions to be released from the surface of an electrode into the adjacent solution. The products of such reactions can interact with biological species undergoing transfer between the electrophoresis gel and blotting membrane, rendering these species chemically modified (e.g., oxidized or reduced), denatured, or nonfunctional. Electrochemical reaction products, especially gases produced by water electrolysis, can also reduce the surface area of electrodes available to transmit current and make electroblotting less efficient.